JPS584464B2 - thyristor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thyristor whose conduction can be switched by supplying a luminous flux.

The ignition of high-power pumps requires considerable circuit expenditure, for example in the case of series connection of a large number of pumps, for example large rectifiers (HGUe valves).

In order to reduce circuit outlays of this kind, it is known to ignite thyristor structures independently of the potential, for example by supplying a luminous flux (for example U.S. Pat. No. 3,697,833). .

However, the known structure has the disadvantage that it does not make optimal use of the light energy used.

Silicon has the drawback of high absorption for light wavelengths of 0.51 μm or less.

On the other hand, the light energy is at least 1.11 eV (λ=1.
1 μm), and thus one electron and one pair of holes must be generated.

The absorption constant of silicon is 2.43eV (λ=0.51μm
) is more than 104 cm-1, and the light beam penetrates the semiconductor structure by 1 μm.

To improve this value, a high energy density infrared light source, e.g. neodymium (YAG with λ = 1.06 μm)
- a laser or a laser with λ=0.89 μm).

The use of lasers of this type involves considerable expense.

Another method of light ignition, indirect light ignition (a photoelectric current amplification element emits light), requires high circuit outlays, as already mentioned.

This is because, on the one hand, the ignition current must be determined from the main circuit, and on the other hand, the voltage of the optoelectronic element must be kept constant, even though the forward voltage varies over three orders of magnitude.

The object of the present invention is to avoid the above-mentioned disadvantages and to provide, for example, a light source which can be ignited by a low-cost light source without requiring a large outlay on circuitry.

Cyrisk needs to be able to be configured by integrating current amplification elements.

Furthermore, it is necessary to be able to easily manufacture this type of cyrisk.

According to the present invention, this problem is solved as follows.

That is, the optical cyrisk includes a semiconductor substrate having at least one end face, a pn junction extending to the region of the end face and having blocking properties in the forward direction, a structure for actuating the thyrisk with light, and an anode-side base region. , a cathode-side base region, the grooved portion including a space charge region at the pn junction, the space charge region extending to the region of the end face when a voltage is applied to the silisk. the pn junction is formed between an anode-side base region and a cathode-side base region, the anode-side base region extending to the end face region in the form of at least one channel through the cathode-side base region; As a result, the pn junction reaches the one end face, and when a forward bias voltage lower than the electron avalanche breakdown voltage of the pn junction is applied to the silicon risk, the pn junction reaches the one end face.
The space charge region of the n-junction penetrates into the anode-side base region by a predetermined distance, and the channel has a diameter equal to twice this predetermined distance and a depth equal to the depth of the p-n junction. ing.

The advantage of this device is that ordinary light with a very small penetration depth, for example visible light from a flash lamp, can be used for igniting the cyrisk.

The light is irradiated directly into the space charge region, and the space charge region that nevertheless appears on the surface does not pose any hindrance to the voltage application at this location.

Light is therefore effectively used to increase the local current density, thereby keeping the required light output low.

The light is absorbed into the space charge region, where electrons and pairs of holes are immediately separated.

Light is avoided to be absorbed in field-free or neutral base regions within the surface, which can increase the charge carrier density proportionally to the useful lifetime.

The present invention will be explained in detail below using the figures.

FIG. 1 is a schematic diagram of a thyrisk structure used for explaining the present invention, and this thyrisk structure includes a p-type base region 1 on the cathode side (within which an n+-type emitter region 2 is provided),
on which a cathode contact K is placed), an n-type base region 3 on the anode side following the p-type base region 1, a p-type emitter region 4 and an anode contact A p+
It has a shape area of 5.

A recess 6 is provided in the p-type base region 1, which extends from the surface of the silisk structure to the extent of the space charge region X/Y of the pn junction between the forward blocking base regions 1 and 3.

The recess 6 has an n+ type region 7 and a P region directly following this region 7.
Surrounded by a +-shaped region 8, these regions 7, 8 are bridged by a common contact 9, in which case an "amplification gate" (for example, N.
/16 issue, pages 128 et seq.) is obtained.

In this type of thyristor structure, when a voltage is applied in the forward direction, the following current density J occurs.

Ji is then the generated current (e.g. thermally generated couple), γ
h and γe represent the efficiency of the pn junction and n+p junction between regions 4/3 and 2/1, and βe and βh represent the transmission efficiency of minority carriers in the neutral region of regions 1 to 3.

Before ignition, J is the current density of the barrier current.

In order to fire the thyristor, the following conditions must be met:

γh (J) βh (J) + γe (J) βe (J) = 1 A simple way to satisfy this condition consists in using the parameter as a function of the current density by increasing the generated current Ji.

This generated current increases steadily with the incidence of light.

Assuming that a generated current density of, for example, IA/crl is required for ignition, the carrier current density is determined by carrier current density (where q is the charge of the carrier).

For example, when starting from a Nd:YAG laser (λ=1.06 μm), there is usually a relatively low doping (N≦10
17 cm-3), an absorption constant of 28 cm-1 is obtained.

The absorption coefficient over the entire length of the 100 μ space charge region is then 0.25.

When each absorbed photon forms a pair of electrons and holes, the power per unit surface area is 3.4 W/cm2.

When irradiating a surface of 1 mm2, the required power is 34 mW.
becomes.

This power must also be supplied within a few μs.

In order to prevent the light from disappearing before the space charge region X/Y is obtained, a recess 6 is provided, which may reach the space charge region.

For high forward voltages, the space charge region or barrier layer is delimited by the dashed line, and for low forward voltages the space charge region or barrier layer is delimited by the dashed line Y.

The width of the space charge region affects the power requirement, increasing the voltage requirement for small forward voltages.

This is because in this case the light beam has to pass through the silicon in order to reach the barrier layer.

For this purpose, the spacing of the recess relative to the barrier layer or space charge region must be selected carefully.

Therefore, this type of silisk structure has a considerable importance on the depth of the recess and is difficult to manufacture.

A particularly advantageous construction according to the invention, which is explained below with reference to FIG. 2, makes it possible to completely avoid the above-mentioned disadvantages.

In FIG. 2, the narrow channel 10 of the weakly doped n-type base region 3 on the anode side reaches the surface of the silice structure of the cathode K region.

Channel 10 has a width B and a depth L from cathode surface 11 to forward blocking pn-junction 13.

At relatively low forward voltages, the space charge region is limited by a line Z (dashed line) along the pn-junction 13 (shown in solid line) between base regions 1 and 3.

The central region of the channel 10 then remains neutral.

If the applied voltage increases, the neutral region shrinks and all channels 10 become empty of charge carriers.

In FIG. 2, such a situation is indicated by the dashed line Y for the average forward blocking voltage and by the dotted line X for the high forward blocking voltage.

The voltage UK required to deplete the channel depends on the shape of the p-type cross section (profile) of the base region 1 and the n-type of the base region 3.
The shape depends on the doping concentration and the channel width B.

By proper selection of these parameters, a predetermined operating characteristic for psi risk can be selected.

If the forward blocking voltage is increased further, the positive voltage of the channel 10 will not increase much with respect to the neutral part of the cathode or p-type region, so that the space charge region will not expand near the surface and also in the p-type base region 1.

Therefore, if the channel depth L is sufficient, even if the forward voltage increases, the neutral p-type region and the surface channel 10
can be maintained at the selected value of the limit voltage UK.

The n+ type region 7 and the p+ type region 8 surrounding the channel 10 and the common contact 9 are integrated elements (
(amplification gate).

The charge carrier pairs generated directly by the light beam applied to the space charge region of the end face 11 separate immediately in the generation of an electric field and a ignition current is formed which, like the usual control electrode current, is passed through the amplifying element 7, 8, 9 and the main thyristor are fired.

For the fabrication of this type of silisk structure, for example weakly n
Covering the shape doped substrate with a mask.

The diameter of the mask is larger than the channel width B (approximately B+2
L), on which a p-type diffusion is performed for the formation of a p-type base 1.

For example, known techniques are suitable for this purpose.

The other parts of the thyristor are also fabricated using known techniques and therefore will not be described further.

The dimensions of the element of FIG. 2 can be determined as follows.

In a conventional thyristor, after a deep aluminum-diffusion is carried out in the n-type substrate, the depth of the channel is L is L=9
It becomes 5 μm.

In the case of Cyrisk, for example, the surface doping concentration of the cathode side base region 1 is NA=1.5·l016 cm-3,
The n-type base-doping concentration of the anode side base region 3 is N
D=6.5·1013 cm-3.

The shape of the doping cross section of base region 1 is N(Z)=N4e
Take the course of rfc(Z/Z0).

However, Z is a position coordinate measured in the vertical direction from the end face 11 to the thyristor, and Z0 is 47 μm.

For this kind of pn-junction (avalanche) breakdown voltage is approximately 2
It is 700V.

At this voltage, the barrier layer or space charge region extends by 35 μm into the p-type region 1 and by 200 μm into the n-type region 3.

The width B of the channel is determined by the permissible potential difference pK on the surface 11 of the silisk between the center of the channel 10 and the p-type region 1.

For example, if UK is set to 190V and the width of the barrier layer of the n-type region of region 3 is 50 μm, the channel width B is 2
×50 μm=100 μm.

In the case of the structure according to the invention, as already mentioned, it is advantageous if the potential curve no longer changes for the voltage between anode A and cathode K.

In practice, the minimum anode-cathode voltage UZ is also important, with which it is possible to fire the thyristor.

According to experiments, it was possible to set UZ to 30V in the above structure.

This means that the recombination of charge carriers on the surface (during the ignition process, the ignition current generated by the light irradiation is reduced) is not important for the above-mentioned structure.

The ignition current does not decrease due to the recombination of charge carriers within the element, due to the diffusion length-dependent transmission efficiency.

To ignite the Cyrisk, e.g. IZ=100mA
ignition current is required.

The number of charge carrier pairs that act as ignition is proportional to the surface F=b.multidot.1 of the barrier layer or space charge region, which surface forms the surface of the end face 11 of the thyristor.

When Uz=30V, the width of the barrier layer of the pn-junction 13 is b=
12.5 μm+21.5 μm=34 μm.

(12.5 μm is the penetration depth into p-type region 1, 21.5 μm
m indicates the penetration depth into the n-type region 3.

) In order to make the area F as large as possible, the line l where the pn-junction 13 intersects the end face 11 of the thyristor is made as long as possible.

A suitable solution for this consists in a comb-shaped structure (FIG. 3) of n-type regions 3 to 10 adjacent to the surface.

If this arrangement has B=100 μm, the length of the pn-junction 13 is 36 mm (p-type base region), the comb-shaped structure being accommodated within the diameter (D=3 mm).

The area F of the barrier layer is approximately 1/6 of the circular area of 0.07 cm2.

For devices of this type, the light source part (imaged onto the area F) used for ignition of the thyristor must emit approximately 2.5·1019 photons per second with an energy greater than 1.1 eV. Must be.

This requires a power requirement of about 16 W (sustained) for a temperature-controlled light source, such as a tungsten wire, which of course lasts for 10-100 μsec. shall be available in flash form for the duration of the period.

It is therefore advantageous to use an arc lamp as the light source.

Of course, advantageous geometric configurations different from that shown in FIG. 3 are also possible.

For example, when the n-type doping of the base region 3 reaches the surface, the regions 10 may not be connected.

[Brief explanation of the drawing]

1 is a side sectional view of a thyristor structure producing light ignition via a recess in the cathode end face of the thyristor blocking in the opposite direction; FIG. 2 is a top view of an advantageously modified thyristor structure according to the invention; FIG. 3 shows a plan view of a thyristor structure according to the invention with a particularly advantageous geometry of the pn junction occurring at the end face. 1...P type base region, 2...N+ type emitter region, 3...N type base region, 4...
...P-type emitter region, 6...Recessed part, 1
3... pn junction.

Claims (1)

[Claims] 1 a semiconductor substrate having at least one end surface 11;
It has a pn junction 13 extending to the region of the end face 11 and having blocking properties in the forward direction, a structure for actuating the cyrisk with light, an anode-side base region 3, and a cathode-side base region 1; The structure includes a space charge region at the pn junction 13, which space charge region extends to said region of the end face 11 when a voltage is applied to the silisk, said pn junction 13 being located at the anode side base. formed between the region 3 and the cathode side base region 1,
The anode side base region 3 is the cathode side base region 1.
extends to said region of the end face 11 in the form of at least one channel 10 passing through said pn junction, so that said pn junction extends as far as said end face 11, with electron avalanche breakdown of the pn junction 13 occurring. When a forward bias voltage lower than the voltage is applied to the sirisk, the pn junction 13
the space charge region penetrates into the anode-side pace region 3 by a predetermined distance, and said channel 10 has a diameter equal to twice this predetermined distance and a depth equal to the depth of the I)n junction. A light cyrisk that is characterized by: